Plasma processing apparatus

ABSTRACT

In a plasma processing method and a plasma processing apparatus, a substrate is processed in a plasma with a surrounding focus ring levitated by the repulsion between a magnet mounted in the focus ring and an electromagnet. The height of the focus ring relative to the substrate support is adjusted to an optimal height by adjusting the current flowing to the electromagnet. Therefore, it is possible to achieve an optimal height of the focus ring for the etching of each layer in a laminated film to enhance the uniformity of laminated film etching and to achieve precise etching.

This application is a division of application Ser. No. 07/644,625, filedJan. 23, 1991, now U.S. Pat. No. 5,213,658.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasma processing method and a plasmaprocessing apparatus, and more particularly to a plasma processingmethod and a plasma processing apparatus for use in production processesfor a semiconductor device, in particular, in an etching process.

2. Description of the Related Art

At present, in a production process of a semiconductor device, plasmaetching and reactive ion etching (RIE), which use a plasma of a reactivegas, are widely used in an etching process to form a fine wiring patternin the submicron line width region.

FIG. 4 is a schematic sectional side view of a conventional reactive ionetching apparatus. Referring to FIG. 4, high-frequency electrodes 3 and4 opposite to each other are disposed in a processing container 7. Acoupling condenser 8 is inserted between the electrodes 3 and 4 andconnected to a high-frequency power supply 9 which supplieshigh-frequency electric power. A reactive gas inlet 5 and a reactiveoutlet 6 for introducing and exhausting reactive gas therethroughrespectively are mounted in the processing container 7. A substrate 1 tobe processed is laid on the high-frequency electrode 3, and furthermore,what is called a focus ring 2, which is a cylindrical insulator, isplaced to surround the substrate 1.

The focus ring 2 functions to enhance the uniformity of progress of theetching reaction on the surface of the substrate 1. In general, theprogress of the etching reaction is slower at the center portion of thesubstrate 1 than at the peripheral portion thereof. This is becauseetching reaction seeds at the center portion of the substrate 1 aredepleted due to the etching reaction and this phenomenon is called theinternal loading effect. The focus ring 2 functions to decrease theprogress and speed of the etching reaction at the peripheral portion ofthe substrate 1, thereby achieving an excellent etching uniformity onthe substrate 1.

It is thought that the etching speed is lowered at the peripheralportion of the substrate 1 by the focus ring 2 since the solid angle ofincidence of the reaction ions onto the substrate 1 is restricted by thefocus ring 2 as the reaction ions are incident nearer the peripheralportion of the substrate 2, than the center or by obstruction of thesupply of neutral radical molecules contributing to the reaction. Thisreveals that the higher the focus ring 2 is, the lower the reactivity atthe peripheral portion of the substrate I becomes. Therefore, the heightof the focus ring 2 is an important parameter for obtaining excellentetching characteristics.

The conventional plasma processing apparatus is composed as describedabove and maintains a predetermined pressure in the processing container7 by introducing a reactive gas, for example, CF₄, CHF₃, Cl₂ or HCl,into the processing container 7 through the gas inlet 5 andsimultaneously exhausting the gas in the processing container 7 throughthe outlet 6. By applying high-frequency voltage from the high-frequencypower supply 9 between the high-frequency electrodes 3 and 4 in thisstate, a plasma in the reactive gas is generated between thehigh-frequency electrodes 3 and 4. At this time, the high-frequencyelectrode 3 on which the substrate 1 is laid is biased with a negativepotential. Therefore, a region, called a sheath, having a strongelectric field is generated between the plasma region and thehigh-frequency electrode 3. The speed of the reactive gas generated inthe plasma is increased by the electric field in the sheath and thereactive gas is incident on the high-frequency electrode 3 and thesubstrate 1 laid on the high-frequency electrode 3. As a result, a thinfilm of, for example, polysilicon, previously formed on the substrate 1,is etched by the reaction of the incident ions.

Since the height of the focus ring 2 is an important parameter forcontrolling the uniformity of etching in the above-described plasmaprocessing apparatus, it is necessary to finely adjust the height inaccordance with process conditions such as the kind of film to beetched, the reactive gas to be used and the amount of high-frequencyelectric power. Furthermore, the recent high density integration ofsemiconductor devices requires uniform etching of a laminated filmformed by laminating two different thin films (for example, a tungstensilicide/polysilicon laminated film or an aluminum alloy/titaniumnitride laminated film).

However, since the focus ring 2 in the conventional plasma etchingapparatus is fixed to the high-frequency electric supply 3 and theheight thereof is constant, it is difficult to simultaneously obtainexcellent etching characteristics of various kinds of thin films byusing a focus ring 2 having a single height. Therefore, it is difficultto uniformly etch a laminated film with a single plasma processingapparatus.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a plasmaprocessing method and a plasma processing apparatus which uniformly etcha laminated film with a single apparatus and obtain an excellent yieldand electrical characteristics of a semiconductor device formed.

In order to achieve the above object, according to one aspect of thepresent invention, there is provided a plasma processing method whichcomprises the steps of: placing a substrate to be processed on ahigh-frequency electrode disposed in a processing container; exhaustinggas in the processing container and introducing reactive gas into theprocessing container; and levitating a focus ring surrounding thesubstrate to be processed and having a magnet therein with the magneticfield of another magnet to a predetermined height while a plasma isgenerated by applying high-frequency electric power to thehigh-frequency electrode so as to process the substrate.

According to another aspect of the present invention, there is provideda plasma processing apparatus which comprises: a processing containerhaving a reactive gas inlet and a reactive gas outlet; a high-frequencyelectrode disposed in the processing container; a high-frequency powersupply connected to the high-frequency electrode; a substrate to beprocessed placed on the high-frequency electrode; magnetic fieldgenerating means for generating a magnetic field in the processingcontainer; and a focus ring disposed surrounding the substrate andincluding a magnet for levitation a predetermined height above the highfrequency electrode by a magnetic field generated by the magnetic fieldgenerating means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a plasma processing apparatusaccording to an embodiment of the present invention;

FIGS. 2 and 3 are schematic sectional views of plasma processingapparatuses according to other embodiments of the present invention; and

FIG. 4 is a schematic sectional view of a conventional plasma processingapparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a sectional view of a plasma processing apparatus according toan embodiment of the present invention. Numerals 1 and 4 to 9 denote thesame components as those in the above-described conventional plasmaprocessing apparatus. In the present invention, permanent magnets 10 areembedded in a focus ring 2A and electromagnets 11 are buried in ahigh-frequency electrode 3A.

In the plasma processing apparatus having the above composition, asubstrate 1 to be processed, on which a laminated film to be etched anda resist pattern are previously formed, is placed on the high-frequencyelectrode 3A. Then, when the electric current is applied to theelectromagnets 11, the electromagnets 11 and the permanent magnets 10buried in the focus ring 2A repel each other and the focus ring 2A islevitated by the magnetic fields and is stationary. At this time, theamount of electric current flowing through the electromagnets 11 is setso that the height of the focus ring 2A is suitable for obtaining thebest uniformity when the uppermost layer of the laminated film (nowshown) formed on the substrate 1 is etched.

Subsequently, a predetermined pressure in the processing container 7 ismaintained by introducing reactive gas, for example, CF₄, CHF₃, Cl₂ orHCl, from the gas inlet 5 and simultaneously exhausting the reactive gasfrom the outlet 6. By applying the high-frequency voltage from thehigh-frequency power supply 9 between the high-frequency electrodes 3and 4 in this state, a plasma of the reactive gas is generated betweenthe high-frequency electrodes 3 and 4. The uppermost layer of thelaminated film is etched in this state. When the etching of theuppermost layer is completed, the high-frequency power supply 9 isturned off, the supply of the reactive gas from the gas inlet 5 issimultaneously stopped so as to stop the etching reaction, and the gasin the processing container 7 is exhausted for a time.

Then, the second layer is etched. In this case it is also necessary onlyto repeat the above operations. In other words, the value of currentflowing to the electromagnet 11 is adjusted, the focus ring 2A isfloated to a position suitable for obtaining the best etching uniformityfor the material of the second layer, the reactive gas is introducedinto the processing container 7, and the high-frequency electric poweris applied between the high-frequency electrodes 3A and 4, so thatplasma of the reactive gas is generated. When the etching of the secondlayer is completed, the etching reaction is stopped by the sameoperations as in the case of the uppermost layer. If the laminated filmhas more than two layers, uniform etching is performed for each layer ofthe laminated film by repeating the above operations a number of timescorresponding to the number of layers of the laminated film.

Although the permanent magnets 10 are embedded in the focus ring 2A inthe above embodiment, electromagnets 12 may be embedded in a focus ring2B as shown in FIG. 2. In this case, the electric power may be suppliedto the electromagnets 12 by pins 13 or the like through electriccontacts 14 mounted in the high-frequency electrode 3A. Furthermore,although the electromagnets 11 are embedded in the high-frequencyelectrode 3A in the above embodiment, as shown in FIG. 3, electromagnets15 may be disposed on both sides of the processing container 7, orelectromagnets 16 may be disposed above the processing container 7.These magnets may be disposed in any position and have the same effectsas those in the above embodiment.

Furthermore, although the plasma etching for a laminated film isdescribed in the above embodiment, it is natural that the presentinvention be applied to the etching of a single film or multistepetching. In order to obtain optimal etching conditions, the height ofthe focus ring 2A may be adjusted during the etching operation itself.

What is claimed is:
 1. A plasma processing apparatus comprising:aprocessing container having a reactive gas inlet and a reactive gasoutlet; a high-frequency electrode disposed in said processing containerfor supporting a substrate; a high-frequency power supply connected tosaid high-frequency electrode; magnetic field generating means forgenerating a magnetic field in said processing container; and a focusring for surrounding the substrate and having a magnet therein forlevitation above the high-frequency electrode by a magnetic fieldgenerated by said magnetic field generating means.
 2. A plasmaprocessing apparatus according to claim 1 wherein said magnetic fieldgenerating means is an electromagnet.
 3. A plasma processing apparatusaccording to claim 2 wherein said electromagnet is embedded in saidhigh-frequency electrode.
 4. A plasma processing apparatus according toclaim 2 wherein said container includes side walls and saidelectromagnet is disposed at a side wall of said processing container.5. A plasma processing apparatus according to claim 2 wherein saidelectromagnet is disposed outside said processing container.
 6. A plasmaprocessing apparatus according to claim 1 wherein said magnet in saidfocus ring is an electromagnet.
 7. A plasma processing apparatusaccording to claim 1 wherein said magnet in said focus ring is apermanent magnet.